cooling the cloud chamber shane spivey uta cloud chamber cooling team
TRANSCRIPT
Cooling the Cloud Chamber
Shane Spivey
UTA Cloud Chamber Cooling Team
Outline
• Brief explanation of cloud chamber
• Motivation
• Design requirements
• Design considerations and tests
• Conclusions
The Cloud Chamber
• Uses a supersaturated layer of vapor to detect ionizing radiation
• Can see tracks of subatomic particles, and study how they bend in a magnetic field
• Using a cloud chamber, Carl Anderson discovered the positron by observing the track it made
Motivation
• To build a working, continuously running cloud chamber for public display in the new Chemistry and Physics building
• To inspire and inform people about the importance of physics
• To gain experience in working with a group to design and construct a large-scale physics experiment
• To bring notoriety to the UTA physics department
Design requirementsfor the cooling system
• Create a temperature gradient of 100° C• Produce a bottom plate temperature of about
70° C• Run in perpetuity• Require only infrequent maintenance• Cost a reasonable amount• Be safe for public interaction• Be aesthetically pleasing
Design considerations:Thermoelectric modules
• Chosen for original 10-layered cloud chamber design• Powered by only electricity• Wafer-thin design• Cooling power too small
Design considerations:Liquid cooling
• Most common method of refrigeration, compression/expansion
• Need liquid with very low evaporation point, like nitrogen• Dangerous and difficult to build
Design considerations:Liquid cooling
• We tested the surface of an aluminum cold plate with liquid nitrogen running through it
Design tests:Liquid cooling, kerosene pump test
• Pump worked but froze up after 10-20 seconds
• We increased the voltage from 3V first using tape and wire, then a DC power supply
• At 12V or higher it didn’t freeze
• At any voltage, the heat from the pump caused the nitrogen to evaporate rapidly
Design tests:Liquid cooling, gravity
• Using a simple gravity setup, the cold plate achieved -70° C after ten minutes
Design considerations:Commercial refrigeration
• Commercially manufactured• By nature, large• Costly, but still cheaper than building it from scratch
Conclusions
• The cooling requirements for a cloud chamber are monumental
• Construction requires expertise as well as equipment and facilities suited to the purpose
• Non-professional job has a high risk of yielding an unsafe end product
• Commercial grade chillers will be more effective, more economical, and safer